Soulknife is bad because it's built around a very specific playstyle (mid-to-close range skirmisher). If you play it as it was intended, it's pretty solid: it's got a good skill list, decent skill points, high HP, two good saves, and a bunch of features which help you not notice how much your full attacks suck (because you're always on the move so you don't make many full attacks).
The "weak" complaints roll in because very few people are satisfied playing the class "as it was intended" -- and they're right. A class which only does one thing and sucks when you try to use it for anything else isn't much of a choice.
The Soulbow PrC fixes a lot of the inflexibility.
As a distinct alternative, take a look at the Warlock (from Complete Arcane) with the Eldritch Glaive invocation (from Dragon Magic).
Cheers, -- N